When you begin your home search you typically want up to date and accurate information on the particular homes you are looking at. And if you have not hired a Realtor yet, your search begins online.
Be careful when looking at the Zillow's site - many time the listings have not been updated. I've had buyers look at a home on Zillow saying it's available and when I've looked it up in the MLS it has in fact sold, not to mention 6 months ago. I have found that Realtor.com is more up to date and accurate as far as current listings when you are not working with a Realtor yet.
Of course the most current information of available homes for sale and homes that have sold is in the Local MLS and can be provided by a Realtor.
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